1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a protection member capable of enhancing reliability against an external impact and preventing outdoor visibility from being lowered due to an external light.
2. Description of the Background Art
Generally, a cathode ray tube (CRT), one of most widely used display devices is mainly applied to a television, monitors of meters, information terminal devices, etc. However, the CRT may cause problems in implementing a compact and light-weighted configuration of electronic devices due to its weight and size.
In order to replace these problems of the CRT, liquid crystal display (LCD) devices having advantages such as a small size, a light weight, and a low consumption power have been actively developed. Recently, demands for flat display devices such as a notebook, a desk top, a large monitor having 30 or more inches, and a wall-mounted TV increase.
The LCD device serves to display images by controlling an amount of light provided from outside. The LCD device is provided with a backlight unit including an additional optical source for irradiating light to an LCD panel. The LCD device is largely divided into an edge type and a direct type according to the position of an optical source with respect to a display surface of the LCD panel. The direct type backlight unit is being widely applied to an LCD device having 30 or more inches, due to its high optical utility, a characteristic to be easily treated, and no limitation in size of the display surface.
However, the direct type backlight unit has the following problems. When a plurality of cold cathode fluorescent lamps (CCFLs) are driven in parallel using one transformer, only some of the CCFLs are driven due to discharge characteristics of the CCFLs. More concretely, the CCFLs have an infinite resistance before being discharged, while having a small resistance due to conductive plasmas occurring in a glass tube after being discharged. Accordingly, once the CCFLs are discharged, an amount of current is increased due to a decreased resistance. That is, when a plurality of CCFLs are driven in parallel, a current flows to CCFLs having a small resistance after being discharged. Accordingly, some of the CCFLs are driven, but others thereof are not driven.
In order to solve these problems, a lamp driving device has been proposed for an LCD device capable of driving a plurality of CCFLs in parallel with using one transformer. According to the lamp driving device, the same equivalent circuit as an external electrode fluorescent lamp (EEFL) is configured by attaching a capacitor having the same capacity (ballast capacitor) onto two electrodes of each CCFL.
Here, the EEFL is lightened by applying an alternate current (AC) to external electrodes. That is, discharge occurs at a discharge space inside a glass tube by an electric field due to a high frequency voltage applied to one pair of external electrodes, thereby emitting ultraviolet rays. Due to the ultraviolet rays, a fluorescent substance deposited onto an inner circumferential surface of the glass tube emits light, thereby emitting visible rays.
FIG. 1 is a sectional view of a direct type LCD device in accordance with the conventional art.
As shown in FIG. 1, the direct type LCD device comprises a backlight unit for providing light; an LC panel 20 disposed above the back light unit and receiving light; polarizers 21 and 22 (or polarizing films) disposed at both side surfaces of the LC panel 20; etc. Here, the backlight unit includes lamps 48 serving as an optical source.
A reflection plate 42 for reflecting light provided from the lamps 48 to a front surface of the LCD device is attached onto a lower cover 41.
Balance PCBs 49a and 49b for coupling the plurality of lamps 48 are provided at both sides of the lower cover 41. Inverter PCBs 50a and 50b for applying an AC voltage are connected to the balance PCBs 49a and 49bm, respectively, which will be explained later.
On the lamps 48, laminated are a diffusion plate 43 for uniformly diffusing light supplied from the lamps 48 and reflected through the reflection plate 42 towards a front surface of the LCD device; and an optical sheet 44 including a prism sheet and/or a protection sheet for compensating an optical function of light that has passed through the diffusion plate 43.
A main support (not shown) for maintaining a balance of an entire force applied to the LCD device is provided. With consideration of the LC panel 20 deposited thereon, the main support is formed to have a certain pattern of steps on an upper side surface thereof.
The LC panel 20 deposited on the main support undergoes a plurality of unit processes. That is, the LC panel 20 includes a thin film transistor (TFT) array substrate 20a having a TFT at each unit pixel, a color filter substrate 20b having a color filter for displaying colors, and an LC injected between the two substrates.
Polarizers 21 and 22 are attached to both side surfaces of the LC panel 20. The polarizers 21 and 22 serve to transmit light vibrating in the same direction as a polarizing shaft among light provided from the backlight unit, while forming light vibrating in one specific direction by absorbing or reflecting light vibrating in other directions with using a proper medium. The polarizers 21 and 22 are essential components of a TN-mode LCD.
An upper cover (not shown) covers an outer edge of the LC panel 20 having the polarizers 21 and 22 attached thereto, and a side surface of the main support. The upper cover is coupled to the lower cover 41 by an additional coupling means such as hooks.
FIG. 2 is a perspective view of a backlight unit in accordance with the conventional art, which shows balance PCBs on the lower cover, and inverter PCBs interworking with the balance PCBs.
As shown in FIG. 2, the inverter PCBs 50a and 50b converts a DC power provided from outside into an AC high voltage. Then, the AC high voltage is applied to balance PCBs 49a and 49b through output connectors of the inverter PCBs 50a and 50b under control of an integrated circuit.
Then, the AC high voltage applied to the balance PCBs 49a and 49b is supplied to ballast capacitors 49al and 49bl through conductive wires and high voltage supply patterns (or wires), thereby making the amount of currents introduced into each tube of the lamps 48 the same. Then, the AC high voltage is introduced into the lamps 48 corresponding to the ballast capacitors 49al and 49bl, respectively.
However, the conventional LCD device may have the following problems. When disposed at a public spot such as an airport or a bus terminal, the LCD device may be damaged due to an external impact, etc., or may have scratches by a malicious user on a thin polarizer attached onto an outer surface of an LC panel with a surface hardness of 3H or less than. In order to solve these problems, additional costs are required, which may degrade the reliability of product.
Furthermore, when the LCD device is disposed under a high level of illumination such as external sunlight or an indoor lamp, if a polarizer attached onto an outer surface of the LC panel does not undergo an additional interface process, a reflectivity of light reflected through the polarizer is 4% to the maximum. When the polarizer attached onto the outer surface of the LC panel undergoes an additional interface process, a reflectivity of light reflected through the polarizer is 1.5% to the minimum. As a result, a contrast ratio of the LCD device is decreased due to its surface reflection. Furthermore, an outdoor visibility of the LCD device is considerably decreased due to a discoloration phenomenon, etc.